Hitherto, in processes for the production of semiconductor devices, for example, IC and LSI, microfabrication has been conducted by means of lithography using a photoresist composition. In recent years, as the degree of integration in integrated circuits increases, it has been requested to form an ultra fine pattern in the submicron region or the quarter micron region. With such a trend, an exposure wavelength tends to become shorter, for instance, from g-line to i-line and further to a KrF excimer laser beam. Moreover, the development of lithography using an electron beam, an X-ray or an EUV beam also proceeds at present in addition to the use of an excimer laser beam.
In particular, the electron beam lithography is regarded as the promising pattern-forming technique of next generation or after the next generation, and positive working resists having high sensitivity and high resolution are being desired. In particular, for the purpose of shortening a wafer processing time, realization of high sensitivity is an important problem. However, in a positive working resist useful for electron beam, when it is intended to pursue high sensitivity, not only a lowering of resolution but deterioration of line edge roughness is caused, and therefore, it is eagerly desired to develop a resist capable of satisfying these performances at the same time. The term “line edge roughness” as referred to herein means a phenomenon wherein an edge between a pattern of resist and an interface surface of substrate irregularly fluctuates in the direction vertical to the line direction due to the characteristics of resist, and therefore, the edge looks uneven when the pattern is observed from just above. Since this unevenness is transferred in an etching step using the resist as a mask and causes deterioration in electric properties, the yield is reduced. In particular, in the ultra fine region of not more than 0.25 μm, the line edge roughness is an extremely important problem to be improved. There is a trade off relation of high sensitivity with high resolution, good pattern profile and good line edge roughness, and therefore, it is very important how these performances are satisfied at the same time.
Also, in the lithography using an X-ray or an EUV beam, it is similarly an important problem to satisfy high sensitivity simultaneously with high resolution, good pattern profile and good line edge roughness, and it is required to solve these performances.
As one of methods for solving such a problem, it is investigated to use a resin having a photo-acid generator (sulfonium group) in a polymer principal chain or side chain (see, for example, JP-A-2-302758, JP-A-4-230645 and U.S. Pat. No. 5,260,410). However, in the investigations in JP-A-2-302758, JP-A-4-230645 and U.S. Pat. No. 5,260,410, since an acid itself generated by the action of exposure is a low molecular weight monomer, there is involved a problem in diffusibility of the acid in a resist film. Thus, it was difficult to attain high resolution and good line edge roughness. On the other hand, it is also investigated to bond an acid generated by the action of exposure to a polymer (see, for example, JP-A-9-325497, JP-A-10-221852, JP-A-2006-178317 and Proc. of SPIE, Vol. 6923, 692312, 2008). However, it is the present state that high sensitivity, high resolution, good pattern profile and good line edge roughness cannot be satisfied at the same time in an ultra fine region.